Given the reduced size of many consumer electronic devices, packaging systems are becoming increasingly important. For example, cellular telephones are becoming smaller and smaller to satisfy consumer's desires for portable lightweight telephones that are easy to carry. Such devices must still provide all the features and functions consumers require. It is typical for a cellular telephone to have a keypad, display, and a sound generator. It is anticipated that the newest telephones will include an infrared (IR) interface, video capability and a fingerprint sensor for added security. Furthermore, the progression to smaller and smaller consumer devices with advanced features is extending beyond cellular telephone technology to such technologies as Personal Digital Assistants (PDAs) and notebook computers
The migration to smaller and smaller devices has placed great emphasis on the various packaging systems used to integrate the various internal system components together within the device housing. However, conventional packaging techniques make use of rigid circuit boards to secure components and to electrically coupled the components together. As a result, limitations exist as to where and how the components can be arranged within the housing and how they are presented at the external surface of the housing to the consumer.
One of the most important issues in electronic packaging is that of packaging and interconnecting integrated circuits (ICs). The ICs are the heart of electronic system controls, and since they are typically sensitive to electrical, mechanical, physical, and chemical influences, they require careful consideration by the packaging engineer. As such, IC packaging is the middle link of the process that produces today's systems.
FIG. 1 shows three levels of electronic packaging. The first level of packaging (IC packaging) is where an IC chip 120 is assembled into an IC package 122. The IC package is the housing that assures environmental protection to the IC chip, and provides for complete testing and high-yield assembly to the next level of interconnection. The IC package provides the first order of interconnection to the IC chip. The IC chip is coupled to external package pins via wire bonding, tape automated bonding (TAB), or using a flip-chip bumping method.
The second level of packaging can be described as IC package assembly onto a carrier circuit board 124. The carrier circuit board is typically made up of a single or multi-layered rigid substrate and is designed to carry the IC package to provide the next level of interconnection to a main printed circuit board (PCB) or back-plane 126.
The interconnecting joints between the IC package 122 and the carrier circuit board 124 is typically made possible via solder balls, IC sockets, and/or solder joint pads. A third level of packaging is accomplished when the carrier circuit board 124 is finally connected to the main (PCB) 126. Thus, current packaging systems provide a system of rigid packaging structures to package and interconnect electronic components.
FIG. 2 shows another conventional technique used to couple an electrical component to a main circuit board. For example, the electrical component may be a fingerprint sensor. The electrical component 102 is mounted to a small rigid printed circuit board 104 that includes a connector 106. The main circuit board 108 also includes a connector 110. An interface cable 112 couples the small circuit board 104 to the main circuit board 108. The interface cable 112 includes mating connectors 114, 116 that mate to connectors 106 and 110, respectively. Thus, the small circuit board 104 and associated connectors 106, 114 are used to couple the component 102 to the main circuit board 108.
Given the above-described packaging system it is easy to see that several limitations exist. For example, connecting the component 102 to the main circuit board 108 is expensive because it requires the small circuit board 104 on which to mount the component 102, and connectors 106, 114 to mate with the interface cable 112. Furthermore, the technique results in size and flexibility limitations because the size of the circuit board 104 and the associated connectors (106, 114) limit how and where the component 102 may be located in a housing, and how such components are presented to the user at the outside surface of the device.
Therefore, it would be desirable to have a packaging system that allows components to be coupled together without the restrictions and limitations that are present in currently available packaging systems.